1. The problem statement, all variables and given/known data You are in a car accelerating forwards. There is a baseball at your feet. Draw two FBDs showing the the ball's motion from the frame of reference of the car and the frame of reference of the sidewalk. Which frame of reference is non-inertial? In which frame do you observe the fictitious force? 2. Relevant equations - 3. The attempt at a solution I don't know what to draw for the FBDs, but I'm confused because I think that both frames are non-inertial and there is a fictitious force in both frames since there is no external force acting on the ball, yet it accellerates backwards from the car and sidewalk's point of view. However, the wording of the question implies that only one frame is non-inertial and only one frame has a fictitious force.